The present invention relates to a mobile communication system, in which wireless land stations and mobile portable wireless terminals do communication, and in which hierarchically designed different kinds of communication sub-systems can share the same radio frequency channel. Particularly, the present invention is applied to a multiple access communication system using CDMA (Code Division Multiple Access).
In order to share the same radio frequency among a plurality of mobile communication systems, according to a conventional art, the systems are prioritized at usage of the radio frequency channel. The systems are categorized into two types, a main system (primary system) and a sub-system (secondary system).
In a specific application of such system, the primary system may be a public mobile communication system (hereinafter called public system) and the secondary system may be a private mobile communication system (hereinafter private system).
Such public system and private system, which are different each other, can not share the same radio frequency channel. Because sharing the same radio frequency channel causes interference between the two different systems. Therefore, even if the method of the wireless communication such as methods of encoding, modulation, demodulation and decoding is the same, different radio frequency channels are allocated to the systems to avoid the interference. For example, different radio frequencies are allocated to a public PHS (Personal Handy-phone System) and a private digital codeless phone system in personal handy-phone communication.
In a first conventional art for sharing the same radio frequency channel between the two systems, the service area and the radio frequency output signal level in the private system are limited to avoid the interference to the public system. However, the distance between the private terminal and the public land station or the distance between the public terminal and the private land station is short, some interference might be caused, even if the output signal level used in the private system is very low.
In a second conventional art, the system is based upon the standard of IS-94 (EIA/TIA/IS-94, xe2x80x9cMobile Station Land Station Compatibility Specification for Analogue Cellular Auxiliary Personal Communication Servicexe2x80x9d, TIA)
FIG. 1 illustrates the system configuration based upon the standard of IS-94. In the figure, reference numeral 11 denotes a public terminal in the public system, 21 a public land station in the public system, 12 a private terminal in the private system, 22 private land stations in the private system, 23 a radio frequency channel scanning station in the private system, 24 a control equipment in the private system, and 25 a PBX in the private system. The scanning station 23 in the private system can receive the radio waves from the public land station 21 and the public terminal 11.
The wireless channel scanning station 23 is to detect what radio frequency channels are used in the public communication system by monitoring the radio waves of the system. By this scanning, the private system can determine the usable radio frequency channel and can share the same radio frequency without interference onto the public system.
First problem of this conventional art is that there is a definite probability to disturb the public communication and it is difficult to guarantee no interference. This depends upon the locations of the wireless channel scanning station 23, the private land stations 22 and the private terminal 12.
FIG. 2 illustrates the problem of the system in FIG. 1, which depends upon the locations of the radio frequency channel scanning station 23, the private land station and the private terminal 12.
Here it is assumed that the private terminal 12 is located near the public land station 21 and the radio frequency channel scanning station 23 is far away from the public land station 21. The private terminal 12 may interfere the public land station 21, even if the radio frequency channel-scanning station 23 confirms no usage of the channel.
In order to solve this first problem, it is necessary to place many radio frequency channel-scanning stations in the service area of the private land station and the terminals. But such way of problem solution is very expensive and eventually it becomes difficult to detect a usable channel.
Second problem of this configuration is that the system with the radio frequency channel scanning station 23 is limited to cellular systems of FDMA (Frequency Division Multiple Access) and TDMA (Time Division Multiple Access) in which there are great number of radio frequency channels and the neighboring land stations do not use the same frequency channel.
FIG. 3 shows the frequency channel structure of the cellular system. In the figure, the same frequency channel is shared at every 7 cells.
In this cellular system, the size of a cell area of the private system is much smaller than that of a cell area of the public system and a radio frequency channel which is not used by a near public land station is permitted to use in order to avoid interference to the public system. Therefore, this system can not be applied to a system by CDMA in which only one channel or a few channels are used.
When a number of systems for mobile communication share the same radio frequency channel in an service area, there is no way other than lowering the radio frequency output signal level of the secondary system or utilizing not used radio frequency channel by the primary system to prevent the interference to the primary system. In each case it is difficult to keep the interference level less than a certain specified level and to guarantee the communication quality of a the primary system.
Lowering the radio frequency output signal level of the secondary system to prevent the interference might cause a difficulty in the communication by the secondary system due to the small output signal level. Utilizing not used radio frequency channel by the primary system to prevent the interference can not be applied to a system by CDMA in which only one channel or a few channels are used.
It is therefore an object of the present invention to provide a mobile communication system with a plurality of systems each of which has a land station and mobile portable terminals capable of communicating with the land station share the same frequency channels, whereby interference by a secondary system is controlled and kept less than a specified certain level for guaranteeing the communication quality in a primary system, and whereby the resource of the radio frequency channel is maximally utilized under the conditions of guaranteeing the communication quality of the primary system.
According to the present invention, a mobile communication system includes a first and second systems. Each of the first and second systems has a land station and at least one mobile terminal capable of communicating with the land station. The land station of the first system has a broadcasting channel transmission unit for transmitting status information via a broadcasting channel, and the mobile terminal of the second system has a broadcasting channel receiving unit for receiving information in the broadcasting channel to obtain a broadcasting channel receiving condition and the status information, a giving interference estimation unit for estimating giving interference level onto communication of the first system by the second system based upon the obtained broadcasting channel receiving condition and the obtained status information, and an output signal level control unit for controlling output signal level of the mobile terminal of the second system based upon the estimated giving interference level.
It is preferred that a plurality of systems are prioritized, and that the first system is a primary system and the second system is a secondary system.
In this case, preferably, the output signal level control unit includes a unit for controlling the output level depending upon traffic condition of the land station of the primary system. Also preferably, the land station of the primary system is connected with a public mobile switch system, and the land station of the secondary system is connected with a private branch exchange system.
It is also preferred that the receiving condition of the broadcasting channel includes receiving signal level from the broadcasting channel, and that the status information includes output level to the broadcasting channel.
It is further preferred that the status information includes communication channel output level from a transmitting system to the broadcasting channel.
It is preferred that the giving interference estimation unit includes a unit for estimating downward radio wave channel propagation loss Ldown from the difference between the output signal level and the received signal level of the broadcasting channel or the access channel.
Preferably, the giving interference estimation unit further includes a unit for estimating upward radio wave channel propagation loss Lup from equation,
Lup=Ldown+Axc3x97log(fup/fdown) (dB),
where A is a constant in the range of 20 to 35, and fup and fdown are frequencies of upward and downward communications.
Also preferably, the giving interference estimation unit further includes a unit for determining giving interference level as a value obtained by subtracting the estimated propagation loss from the output level to the broadcasting channel or the access channel.
According to the present invention, also, a mobile communication system includes a first and second systems. Each of the first and second systems has a land station and at least one mobile terminal capable of communicating with the land station. The land station of the first system has a broadcasting channel transmission unit for transmitting status information via a broadcasting channel, an access channel receiving unit for obtaining given interference level information sent via an access channel, and an output signal level control unit for controlling output signal level of the land station of the first system based upon the obtained given interference level information, and the mobile terminal of the second system has a broadcasting channel receiving unit for obtaining broadcasting channel receiving condition and status information, a given interference estimation unit for estimating given interference level onto communication of the second system by the first system based upon the obtained receiving condition and the obtained status information, and an access channel transmission unit for transmitting the estimated given interference level information to the land station of the first system.
It is preferred that a plurality of systems are prioritized, and wherein the first system is a secondary system and the second system is a primary system.
In this case, preferably, the output signal level control unit includes a unit for controlling the output level depending upon traffic condition of the land station of the primary system. Also preferably, the land station of the primary system is connected with a public mobile switch system, and the land station of the secondary system is connected with a private branch exchange system.
It is also preferred that the receiving condition of the broadcasting channel includes receiving signal level from the broadcasting channel, and that the status information includes output level to the broadcasting channel.
It is further preferred that the status information includes communication channel output level from a transmitting system to the broadcasting channel.
It is preferred that the given interference estimation unit includes a unit for estimating downward radio wave channel propagation loss Ldown from the difference between the output signal level and the received signal level of the broadcasting channel or the access channel.
Preferably, the given interference estimation unit further includes a unit for estimating upward radio wave channel propagation loss Lup from equation,
Lup=Ldown+Axc3x97log(fup/fdown)xe2x80x83xe2x80x83(dB),
where A is a constant in the range of 20 to 35, and fup and fdown are frequencies of upward and downward communications.
Also preferably, the given interference estimation unit further includes a unit for determining given interference level as a value obtained by subtracting the estimated propagation loss from the output level to the broadcasting channel or the access channel.
According to the present invention, further, a mobile communication system includes a first and second systems. Each of the first and second systems has a land station and at least one mobile terminal capable of communicating with the land station. The land station of the first system having a broadcasting channel transmission unit for transmitting status information via a broadcasting channel, an access channel receiving unit for obtaining receiving condition and status information from the mobile terminal of the second system via an access channel, a giving interference estimation unit for estimating giving interference level onto communication of the second system from the first system based upon the obtained receiving condition and the obtained status information, and an output signal level control unit for controlling output signal level of the land station of the first system based upon the estimated giving interference level, and the mobile terminal of the second system having a broadcasting channel receiving unit for obtaining the broadcasting channel receiving condition and the status information, and an access channel transmission unit for transmitting the obtained receiving condition and the obtained status information via the access channel to the land station of the first system.
It is preferred that a plurality of systems are prioritized, and that the first system is a secondary system and the second system is a primary system.
In this case, preferably, the output signal level control unit includes a unit for controlling the output level depending upon traffic condition of the land station of the primary system. Also preferably, the land station of the primary system is connected with a public mobile switch system, and the land station of the secondary system is connected with a private branch exchange system.
It is also preferred that the receiving condition of the broadcasting channel includes receiving signal level from the broadcasting channel, and that the status information includes output level to the broadcasting channel.
It is further preferred that the status information includes communication channel output level from a transmitting system to the broadcasting channel.
It is preferred that the giving interference estimation unit includes a unit for estimating downward radio wave channel propagation loss Ldown from the difference between the output signal level and the received signal level of the broadcasting channel or the access channel.
Preferably, the giving interference estimation unit further includes a unit for estimating upward radio wave channel propagation loss Lup from equation,
Lup=Ldown+Axc3x97log(fup/fdown)xe2x80x83xe2x80x83(dB),
where A is a constant in the range of 20 to 35, and fup and fdown are frequencies of upward and downward communications.
Also preferably, the giving interference estimation unit further includes a unit for determining giving interference level as a value obtained by subtracting the estimated propagation loss from the output level to the broadcasting channel or the access channel.
According to the present invention, in addition, a mobile communication system includes a first and second systems. Each of the first and second systems has a land station and at least one mobile terminal capable of communicating with the land station. The land station of the first system has a broadcasting channel transmission unit for transmitting status information via a broadcasting channel, an access channel receiving unit for obtaining receiving condition and status information from the mobile terminal of the second system via an access channel, a given interference estimation unit for estimating given interference level onto communication of the first system from the second system based upon the obtained receiving condition and the obtained status information, and a discrete control channel transmission unit for transmitting commands to control the output signal level of the mobile terminal of the second system based upon the estimated given interference level via a discrete control channel, and the mobile terminal of the second system has a broadcasting channel receiving unit for obtaining the broadcasting channel receiving condition and the status information, an access channel transmission unit for transmitting the obtained receiving condition and the obtained status Information to the land station of the first system via an access channel, a discrete control channel receiving unit for obtaining the commands to control the output signal level, and an output signal level control unit for controlling output signal level of the mobile terminal of the second system based upon the obtained commands.
It is preferred that a plurality of systems are prioritized, and that the first system is a primary system and the second system Is a secondary system.
In this case, preferably, the output signal level control unit includes a unit for controlling the output level depending upon traffic condition of the land station of the primary system. Also preferably, the land station of the primary system is connected with a public mobile switch system, and the land station of the secondary system is connected with a private branch exchange system.
It is also preferred that the receiving condition of the broadcasting channel includes receiving signal level from the broadcasting channel, and that the status information includes output level to the broadcasting channel.
It is further preferred that the status information includes communication channel output level from a transmitting system to the broadcasting channel.
It is preferred that the given interference estimation unit includes a unit for estimating downward radio wave channel propagation loss Ldown from the difference between the output signal level and the received signal level of the broadcasting channel or the access channel.
Preferably, the given interference estimation unit further includes a unit for estimating upward radio wave channel propagation loss Lup from equation,
Lup=Ldown+Axc3x97log(fup/fdown)xe2x80x83xe2x80x83(dB),
where A is a constant in the range of 20 to 35, and fup and fdown are frequencies of upward and downward communications.
Also preferably, the given interference estimation unit further includes a unit for determining given interference level as a value obtained by subtracting the estimated propagation loss from the output level to the broadcasting channel or the access channel.
Further objects and advantages of the present invention will be apparent from the following description of the preferred embodiments of the invention as illustrated in the accompanying drawings.